J1.5:Timezones parameter type
From Joomla! Documentation

Parameters have been superseded by form fields in Joomla! 1.6. You may want to use the corresponding Timezone form field type. |
The timezones parameter type provides a drop down list of time zones. If the parameter has a value saved, this value is displayed when the page is first loaded. If not, the default value (if any) is selected.
- type (mandatory) must be timezones.
- name (mandatory) is the unique name of the parameter.
- label (mandatory) (translatable) is the descriptive title of the field.
- default (optional) (translatable) is the default time zone. For example, use '-10' for '(UTC -10:00) Hawaii'.
- description (optional) (translatable) is text that will be shown as a tooltip when the user moves the mouse over the drop-down box.
Example XML parameter definition:
<param name="mytimezone" type="timezones" default="-10" label="Select a timezone" description="" />